1. Field of the Invention
The present invention relates to an open ear canal hearing aid system, and more particularly to an open ear canal hearing aid system including a sound processor for amplifying sounds included within a predetermined amplitude and frequency range and means for transmitting sounds to the ear canal and for receiving sounds which are in the ear canal.
2. State of the Art
Present day hearing aids have been developed to correct the hearing of users having various degrees of hearing impairments. It is well known that the hearing loss of people is generally not uniform over the entire audio frequency range. For instance, hearing loss for sounds at high audio frequencies (above approximately 1000 Hz) will be more pronounced for some people with certain common hearing impairments while hearing loss for sounds at lower frequencies (below approximately 1000 Hz) will be more pronounced for people having different hearing impairments.
The largest population of people having hearing impairments includes those having mild hearing losses with normal hearing in the low frequency ranges and hearing losses in the higher frequency ranges. In particular, the most problematic sounds for people having such mild hearing losses are high frequency sounds at low amplitudes (soft sounds).
Conventional hearing aids employ electronic hearing aid devices. Through various signal processing techniques, sounds to be delivered to the ear are rebuilt and supplemented to facilitate and optimize the hearing of the user throughout the usable frequency range. However, these devices block the ear canal so that little or no sounds reach the ear in a natural, unaided manner. Furthermore, such devices have drawbacks, such as feedback, when used with communication devices such as telephones.
Conventional hearing aids generally provide adequate hearing throughout the entire speech frequency range for most hearing impairments. However, these types of devices are not optimal for people having mild hearing losses for a number of reasons. Conventional hearing aids can unnecessarily amplify loud sounds so that these sounds become uncomfortable and annoying to the mild hearing loss users. In many hearing aids, such loud sounds are also distorted by the sound processing circuitry, significantly reducing the intelligibility of speech or the quality of other sounds. In addition, these types of hearing aids introduce phase shifts to received sounds, resulting in a reduction of the user's ability to localize sound sources. These hearing aids can therefore degrade certain sounds that the mild hearing loss user could otherwise hear adequately without any aid. Additionally, these traditional hearing aids are overly complicated and burdensome to users having mild hearing losses.
Efforts have been made to provide different gains for sounds of different frequencies, depending on the hearing needs of the user. For example, U.S. Pat. No. 5,276,739 to Krokstad discloses a device which amplifies sounds with different gains according to the frequencies of the sounds. While this device provides an improved gain response, it processes sounds across the entire frequency range, including low frequency sounds. Thus, this device suffers from the same problems noted above in accommodating the mild hearing loss user.
Other attempts to provide different gains for sounds of different frequencies employ multiband compression in which sounds of different frequency bands and different amplitudes are compressed by different amounts. For example, U.S. Pat. Nos. 5,278,912 and 5,488,668 to Waldhauer disclose multiband compression for hearing aids. Such systems apply compression to the entire frequency range, including low frequency signals. In the case of a user with mild hearing loss, compression for low frequency sounds is not needed. Applying compression to low frequency sounds thus results in a waste of money and space for the circuitry required to perform such compression and unnaturally and unnecessarily increases the amplitude of low level sounds.
Conventional hearing aid systems cause an additional problem known as the occlusion effect. The occlusion effect is the increased loudness of certain sounds due to transmission of sound by tissue conduction when the ear canal is blocked and air conduction is impeded, resulting in sounds which are both unnatural and uncomfortable for the user. In particular, the user's own voice sounds different than normal when the ear is blocked.
Vents have been introduced in hearing aid systems to provide pressure relief and to shape frequency responses. The vents are not designed to let sounds into the ear canal and do little to improve the occlusion effect. The occlusion effect therefore remains another drawback to using these traditional hearing aid systems.
In an effort to alleviate some of the aforementioned problems, some behind-the-ear (BTE) aids have been designed with a special tube fitting. These types of aids include a tube that extends into the ear canal and is held in place by an ear mold that leaves the ear canal generally unobstructed. The relatively open ear canal overcomes some of the problems mentioned above. However, these types of aids suffer from a number of other significant problems.
For example, like other BTE hearing aids, the "tube fitting" aids typically employ a rigid ear hook that connects to a soft tube which in turn connects to a rigid ear mold. The tubing is straight, but has the disadvantage that the tube does not hold the device in place. The result is that this type of BTE hearing aid requires a large ear hook and a large, hard, close-fitting ear mold to maintain the position of the tube within the ear canal. The large size of these components results in a cosmetically unattractive device. Also, the ear mold has to be custom-manufactured, which adds to the cost of the device and the time needed to fit the hearing aid.
U.S. Pat. No. 4,904,708 to Gorike discloses another type of hearing aid device in which the hearing aid is formed in a pair of eyeglasses. One drawback of this configuration is that the user is required to wear a custom made pair of eyeglasses, which adds to the cost of the device.
Another problem with these BTE devices is the fact that the microphone is located behind the ear. The microphone can have trouble picking up sounds from various directions because of being located behind the ear. In addition, the microphone can pick up too much background sound such as hair rubbing on a shirt when the user turns his/her head.
None of the above-described systems are directed to a hearing aid system which specifically solves only the hearing needs of people having mild hearing loss. Because people with mild hearing loss have normal hearing for many sounds, it is desirable to provide a hearing aid system which allows these sounds to pass through the ear canal unaided and to be heard in a natural manner and to only compensate and aid the sounds that the user has difficulty hearing. It is further desirable that such a hearing aid be cosmetically attractive and comfortable to wear while providing better sound pick-up for the microphone.